Thread rolling head



Aug- 12, 1941- M. w. LAMPRECHT ETAL 2,252,130

THREAD ROLLING HEAD Filed Feb. 13, 1939 4 Sheets-Sheet 1 l INVENTORS MERLE W. LAMPRECHT & HAROLD N. ANDERSON ATTO All@ 12, 1941- M.`w. LAMPREcH-r ET AL 2,252,130

THREAD ROLLING HEAD Filed Feb. 1.31939 4 Sheets-Sheet 2 F IG.- 4

Fla-3 FIG.- 6

INVENTORS LAMPRECHT 8.

ANDERSON MERLE W. HAROLD N.

.Aug- 12, 1941- M. w. LAMPRECHT 'a1-AL 2,252,130

THREAD ROLLING HEAD Filed Feb. 13, 1959 4 Sheets-Sheet 3 lNvEN-roRs MERLEW. LAMPRECHT 8. HAROlD N. ANDERSON Aug, 12, 1941. l l

M. w. LAMPRECHT ETAL THREAD ROLLING HEAD Filed Feb. 13, 1939 4 SheetsSheet 4 l Rs MERLE W. LAMPRECHT 8. HARgID N. ANDERSON www? Patented Aug. 12, 1941 THREAD ROLLENG HEAD Application February 13, 1939, Serial No. 256,106 c claims.' `(ci. sc-im This invention relates to improvements in apparatus for rolling threads in substantially cylindrical blanks.

We are aware that it is not broadly new to roll threads into cylindrical blanks but Asuch threads heretofore produced have not been sufciently accurate and well nished to be satisfactory for all purposes. Our improved apparatus is so constructed and arranged that it provides a screw thread equal to and indeed superior to threads formed by any other means, both as to strength and accuracy and is capable of producing such threads not only in softer metals but also in steel and this with long life of the thread rolling apparatus. The features of our apparatus which make these` results possible will be hereinafter set forth in greater detail.

One of the objects of the present invention is to provide roller dies for rolling the threads into a blank wherein the work of deforming the thread in the blank is divided amongst a plurality of ribs on the roller dies, preferably among three or more ribs so as to accurately form the thread on the blank and to give long life to the dies.

Another object of the present invention is to provide a plurality of roller dies mounted in a rotatable head which is adapted to receive the work blank axially of the head and wherein the ribs of each of the roller dies deepens the thread groove rolled into the blank by the preceding corresponding rib on another roller die. This is what we have hereinafter called the step-bystep formation of the thread wherein the work of producing the thread is divided up substantially equally between two or more roller dies.

A novel feature of the present invention is the provision of thread rolling dies mounted in a ro tatable head, said dies being rotatably mounted on anti-friction bearings to reduce the friction between the die ribs and the work blank which is necessary to rotate the separate dies. This feature combined with the spreading of the metal deforming load over a plurality of die ribs so reduces the load on the rib faces that long life of the dies and accurate work is assured.

Certain features of our invention are applicable to that type of apparatus in which the roller dies have annular ribs and the dies are set on an axis to the blank corresponding to the helix angle of the thread to be rolled, or equally applicable to a similar type of apparatus where the roller dies are set on axes parallel to the axis of the blank and the roller dies are provided with helical ribs corresponding to the thread to be formed in the blank.

Another feature of our invention is the provision of novel means for supporting the blank at a point where the ribs on the roller dies first engage the blank.

Another feature of the present invention isv the provision of means for truing up the size of the cylindrical blank just before it enters the thread rolling ribs of the roller dies.

' Another novel feature of our apparatus is the provision of means for simultaneously moving a plurality of roller dies radially inwardly and outwardly relative to the axis of a rotatable head and for locking the dies in various adjusted positions so as to set the same dies to roll threads on blanks of Varying diameters as desired. At the same time means is provided for rapidly moving the roller dies radially inwardly and outwardly of a rotatable head for the purpose of gripping or releasing the blank worked upon. These adjustments of the dies can be Ina-de without stopping rotation of the head.

Our invention also provides in a rotatable head' carrying a plurality of roller dies each having a' helical thread, novel meansfor insuring coordinated rotation of the roller dies insuring that the proper portion of each roller die traverses the thread formed on the work blank. In such a device we so arrange this coordinating means as to permit the opening and closing of the dies upon a blank without losing the proper coordinated relationship between the dies.

Other features of our invention include the speciiic arrangement of the parts whereby we insure accurate reproduction of the thread desired, together with ruggedness of construction whereby accurate work is turned out over long periods of time without excessive repairs and the convenient and simple arrangement of the parts forV ease of adjustment, and other novel features as will be apparent from the accompanying drawings and specification.

Inthe drawings,

Figs. l and 2 are side and end elevations respectively of a head equipped with one embodinient of our thread rolling invention, Fig. 1 being Vpartly a central longitudinal section taken along the line l-l of Fig. 2.

Fig. 3 is an end view of the die ring. Y

Fig. 4 is a sectional View of the same taken along the line 4--4 of Fig. 3.

Fig. 5 is an end view of the barrel of the rotatable head.

Fig. 6 is a side elevation of the barrel of Fig. 5.

Figs. 7 and 8 are end and side elevations respectively of a roller holder block.

Fig. 9 is a side elevation of a roller holder.

Fig. 10 is a bottom view of the roller of Fig. 9.

Fig. 11 is an enlarged sectional View of one of the rollers of Fig. 1.

Fig. 12 is a very much enlarged diagrammatic y view superimposing the profiles of a plurality of roller dies.

Fig. 13 is a view similar to Fig. 12 superimposing the profiles of a plurality of roller dies of a modied form.

Fig. 14 is an enlarged sectional view of a portion of one end of a roller die embodyinganother feature of our invention.

Figs. 15 to 19 relate to a modified form of our invention wherein the roller dies are provided with helical ribs; Fig. 15 is a view of the rotatable head similar to that shown in Fig. 1 but carrying a different type of die; Fig. 16 is a sectional view taken along the line lli-I6 of Fig 15; Fig. 17 is an enlarged side elevation of one of the rollers of Fig. 15; Fig. 18 is an end view of the same; and Fig. '19 is a diagrammatic view showing the interplay between certain parts of Fig. 16 enlarged, an adjustable relationship of the parts is here shown in dot-dash lines; while Fig. `2.0 is a view of a face plate.

One of the valuable features of our invention is that we have embodied the same in a head adapted to be mounted upon a machine of the type adaptedto' produce threads by cutting. For instance we have shown our head here adapted to a Model 35 threading machine made by the Acme Machinery Company. Such a machine has a bed 2|r carrying ways upon which a tailstock or the like may be mounted for sliding movement longitudinally of the machine. Mounted at one end of the frame is a housing 22 carrying a suitable drive shaft 23 driven by means of the pulley 24 or otherwise as may be desired. This shaft drives through suitable gearing a gear 25 mounted on a spindle 26 which extends outside of the housing for attachment to our novel thread rolling head.

The head and its parts shown in Figs. 1 to 10 comprises a barrel 27 best shown in Figs. 5 and 6 which carries an internal thread 28 at one end for attachment to the spindle 2B. The barrel has a central opening at 29 extending axially thereof to receive the blank to be threaded. It will be understood that in this type of machine a hollow space is provided through the apparatus housed in thehousing 22 in alinement with the opening 29 so that if desired a long blank may be threaded. The barrel is provided with a centrally located bushing of tool steel or the like within the opening 23. The barrel is also provided preferably with tool steel strips which set in thenotches 30 on the outer circumferential surfacevof the barrel for accurately maintaining the relative position of the barrel and the parts encircling it in case of wear. The forward end of the barrel is provided with a plurality of slots or pockets 3l extending radially of the barrel from its circumference into the center. The slots 3| are for the reception of the roller holder blocks 38 later described and the slots are preferably lined with tool steel bushings, one o f which is shown in section at 3|a in Fig. 1.

Slidably mounted upon and encircling the barrel is a die ring 32 which is best seen in Figs. 3 and 4. 'Ihis ring has an internal bore 33 at its rear end adapted to fit closely about the barrel 21. It also carries a keyway 34 extending parallel to the axis of the ring and adapted to receive the key 35 which is rigidly secured in the outer face of the barrel 2l. This secures the die ring and barrel against relative rotation while permitting relative movement axially. The die ring is provided on its internal face with the longitudinally extending slots 36 in which are secured tool steel strips for insuring against wear. Spaced apart on the die ring and opening inwardly thereof are the inclined pockets or guides 3'! for receiving and coacting with the roller holder blocks 38 of Fig. 8. These pockets 3l' are of greatest diameter at the forward end of the die ring and have outer surfaces which slope therefrom longitudinally and inwardly, all of the guide surfaces 31a being inclined equally toward the axis of the die ring. In actual practice the interior surfaces of these pockets are provided with tool steel bushings, a portion of which is shown at 37o in Fig. l. Each of the pockets or slots 3'! is of T-shape having the wider portions Slb located radially outwardly of the pockets and adapted to receive the wings 38a at the outer edges of the roller holder blocks. Thus the roller holder blocks are held in the die ring while permitting relative longitudinal movement between them. Such relative longitudinal movement will be later described and serves to move the blocks radially inwardly and outwardly of the thread rolling head. The ring 32 has an annular groove 32a about the rear end thereof for purposes of accommodating a shifting yoke which will be later described.

The roller holder blocks, of which there are three all alike, are formed as shown in Figs. 7 and 8. They have the inclined wing projections 38'a extending along their outer edges and adapted to engage in the T-hape slot formations 31h in the die ring 32. The portion 33h is of a width to slide in the narrower portion of the T-shape slots 31 of the die ring. The portion 38e ts within the bushing-lined slots 3i of the barrel 21. The rear faces of the block portions 38e engage against the bushings Sia as indicated in Fig. 1. The forwardly facing surfaces 39d of the blocks 38 engage against a face plate 39 which is best seen in Fig. 2() and is shown in assembled position in Fig. 1. This face plate is secured to the forward end of the barrel 27 by suitable screws which enter alined openings shown in Figs. 5 and 20. The face plate S9 has three outwardly opening slots 39a which receive the portions 38h of the blocks 33 and permit a certain amount of radial movement inwardly and outwardly of the blocks.

A roller holder it is secured to each block 38. There are three of these holders, which are all alike and best shown in Figs. 1, 9 and l0. The radially outward portion lila of each holder has a surface lil adapted to engage the face 42 of block 38 and to be secured thereto by screws entering the openings 43 of holder i8 and 44 of the block 38. Side wing portions 46h engage the opposite side faces of the block 38. The holder 4D also has a face 45 at right angles to the face 4I which is adapted to engage the face 46 on the block 38. Here again wing portions Mic engage the opposite side faces of the portion 38h of block 3`8. The roller holder is thus firmly secured to the block 38 which in turn is rigidly held as will later appear. The radially inward portion of the holder 4l? is bifurcated as best seen in Figs. 1 and 9 providing the arms Mld which carry alined openings 4l and 38 for receiving the ends of a shaft 49 which in turn carries a roller 50. The openings 4l and 48 are circular, half being in the arms 40d and the other half being in the bearing caps I and 52 which are secured to the arms 49d by suitable screws in the well known manner.

The rollers 59, of which there are three, are in this modification rotatably mounted on the shafts 49 with bearings 53 lying between them. It will be appreciated that the load on each roller die is very heavy when rolling threads in steel bars. The force for turning the roller dies comes from the friction developed between the die ribs and the blank being threaded. Thus, if the dies rotate on plain bearings .a heavy load is placed on the die ribs with consequent heavy wear on the ribs and inaccurate flow of the metal of the blank during the thread rolling operation. To reduce the load the anti-friction bearings 53 are provided. This feature, taken with the division of the metal deforming load among several ribs on the dies, so reduces the work required that only about sixty A:toot-pounds is developed as torque on the bar or blank when rolling an eight pitch thread on a one-inch steel bar. The motor driving the threading head during this operation takes only 11/2 amperes at 220 volts. Washers 54 lie between the rollers and the arms 49d and retain the bearings 53 in place. A snap ring 55 may be used to hold the parts in place on shaft 49 during an assembly operation.

Each roller 50 has ribs 56 annularly arranged upon its outer surface .and these ribs must be supported at the proper angle to the axis of the head in order to produce threads at the proper angle upon the blank to be threaded. To

this end the openings 41 and 48 are arranged in 5 the arms 40d of the roller holders so as to position each shaft 49 at the angle B relative to the line 51 (which is parallel to the axis of the blank), which angle B corresponds to the helix angle of the thread to be formed upon the work blank. Naturally this angle will vary for blanks of different diameters but we obtain satisfactory results by selecting the angle B as a compromisefor several blanks of different diameters adapted to be threaded with the same set of roller dies. Satisfactory results are thus achieved.

The mechanism for shifting the die ring 32 relative to the blocks 33 so as to move the roller dies radially inwardly and outwardly of the head is best seen in Figs. 1 and 2. A yoke 58 has r larms which pass around opposite sides of the barrel 21 and which carry pins j59 which engage in the annular slot 32a of the die ring 32. The yoke is supported at its upper end by a swivel block 6i) which has threaded engagement with a screw 6l which is adjustable longitudinally of the thread rolling head by 4means of the hand wheel 62 such adjustment being indicated as to rough adjustment on the scale 63 and as to ne adjustment by a Vernier scale on disk 63a 1ocated at the front of the machine. The lower end of the yoke is pivotally connected at 64 with a toggle 65, the link 65a of which is rigidly mounted on a shaft 66 which has a fixed position in the housing 22. A handle 61 on shaft 66 serves for straightening of the toggle 65 so as to cause the die ring 32 to move forwardly or toward the left as viewed in Fig. 1, thus causing the blocks 38 to move radially inwardly because they are constrained against longitudinal movement by their rposition in. pockets 3l between the face plate 39 and the bushing 31a. A bar 68 pivotally connected to a crank arm 69 on shaft 65 carries a spring 10 which acts through arm 69 on shaft 66 always in a direction to turn link 65a in a counterclockwise `direction as viewed in Fig. 1. Thus the tendency of this spring is always to return the toggles 65 to broken position to cause yoke 58 to move backwards or toward the right as viewed in Fig. 1. This causes opening movement of the roller dies radially outward. The toggle 65 in the locked position of Fig. 1 (corresponding to a threading operation of the rolling head) is just short of straightened position and is so held by a dog 1| which is pivotally mounted at 12 on the frame and is held in locking position by a spring 13. The dog has a shoulder which engages a suitable shoulder rigid with shaft 66 and indicated at the point 14.

Suitable means is provided for limiting the opening movement of the dies in the head. In the embodiment illustrated a rod 15 is pivotally connected to the lower end of the yoke, which rod carries near the tail end of the machine an adjustable abutment which engages against a portion of the frame when the head has opened suliciently to permit withdrawal of the blank being worked upon.

Means may be provided for automatically opening the die head at the termination of a threading operationif desired. It will be understood that in rolling a thread on a blank one end of the blank is engaged between the roller dies 5D while the other end is clamped in a tailstock movable along the bed of the machine. This tailstock may carry a suitable bar (not shown) which is so adjusted that when it is desired to terminate the threading operation the bar will engage the surface 11a on latch 1| thus moving the latch upwardly and permitting spring 1i? to cause opening of the die head.

It will be seen from the above description that relative movement between the die ring 32 and the blocks 38 is used for two purposes. In the rst place adjustment of the swivel block E9 along the thread 6l positively sets the locked position of yoke 53 and collar 32 so that when the parts are in the position of Fig. 1 the roller dies 59 are positively located with respect to the axis of the head so as to roll a thread of selected diameter. At the same time once that adjustment at Sil, 6| has been set then the control of shaft 66 either manually or automatically serves to throw the roller dies outwardly at the termination of a threading operation. It will be obvious that for repeated threading operations on blanks of the same diameter the adjustment at 69, 6| will be rst made and thereafter the toggle will be manipulated at the beginning and ending of each threading operation.

Referring now more in detail to the profile of the roller dies 5I] which as above stated in this embodiment carry annular ribs upon their circumferences, a lclearer understanding of the principle upon which our apparatus works will be gathered from Figs. 11, 12 and 13. Attempts have been made heretofore to roll threads in cylindrical blanks using apparatus in some respects similar to ours but such apparatus did not work efficiently, probably because the profile of the die rib entering the blank was not of a form to deform the metal in the most eicient manner or the work of deforming the metal was placed on one rib or such a small number of ribs that the roller die broke ydown very quickly and ceased to perform efficiently in practical oper-ations. We have -chosen to illustrate our improved apparatus as used in forming a U. S. standard thread but it will be understood that the principles here disclosed may be utilized in the formation of other threads.' `To this end we have formed the ribs of the roller dies 50 yas shown somewhat enlarged in Fig. 11 and greatly enlarged in the diagram of Fig. 12. Itwill be noted that each of the ribs has flanks l converging toward the crest 11a, b or c at an angle of 60 to each other. This is a very eiiicient form of rib lproiile for getting the best metal deformation with the minimum of friction. We also use a plurality of ribs to deformY the thread to its root diameter so as to divide the load and the friction among a number of ribs, preferably three or more so that the deformation of the metal of the blank is not too violent or accompanied by too great friction. Those familiar with this art will readily comprehend that where the friction between the die ribs and the blank is too great the metal will flow away from the crest I1-a, b or c of a rib inwardly along the flanks 16 to such an extent as to raise the material adjacent each rib higher than the material of the blank between such points. In other words it will leave somewhat of a groove in the blank at the mid point between two deforming ribs. This groove will be carried clear out to the -crest of the threads formed on the blank and will leave an imperfect form of finished thread.

One manner of carrying out the purpose of our invention is illustrated in Fig. 12 wherein we have superimposed the profiles of three roller dies 50 although it will be understood that in actual practice these dies are spaced 120 apart about the axis of the threading head. It will also be understood by those slL'lled in this art that the ribs'on the different dies are so placed about the axis of the head that their portions nearest the axis of the head lie along a helical path. In other words if one of the rollers hereinafter called the first roller, is the iirst to engage the blank, then the next encountered roller hereinafter referred to as the second roller, is set sufficiently toward the rear of the head to follow in the same helical thread depression started by the first roller. In a similar manner the third roller has ribs which follow in the same helical path traced by the ribs of the first and second rollers. In the diagram of Fig. 12 the profile of the first roller is shown in ful-l lines, that of the second roller in dot-dash lines, and that of the third roller in dash lines. A suitable blank for use in a threading head of this type is a cylindrical blank having the pitch or effective diameter of the thread to be formed. In other words it is of a diameter equidistant between the root or core diameter of the thread to be formed and the outside or crest diameter of the thread to be formed. Preferably We so arrange the positioning ofthe roller dies 59' in the threading head with reference to the blank to be threaded so that the crests 11a, b and c of the first rib on each roller shown at 11a, 'Hb andv'l'lc, firmly engage Without appreciably entering the surface of the blank. The second ribs on the various rollers as shown at 18a, 'leb and 18o then have crest Aradii equal to the radius at the crest 'Vl plus one-sixth of the depth of thread to be formed on the blank. In a similar manner the rib crests shown at 19 add to the radius at crests 'I8 one-sixth of the depth of thread, and the crests indicated at 80a, b and c add an additional one-sixth of the depth of thread. It will thus be seen that in three steps. namely, 18a, b and c, 19a, b and c and 80a, b and c, the ribs of the roller dies have entered beneath the original surface of the :cylindrical blank by one-half the depth of the thread to be formed, during which operation the material ofthe blank has been deformed outwardly between the ribs of the roller dies to fill in the grooves between them so that when the ribs a, b and c have fully deformed the metal of the blank, that metal will have been deformed outwardly to the points indicated at 8l, thus forming the finished crest on the thread of the blank While the ribs at 80a, b and c put the finished profile at the root diameter of the thread formed onv the blank. Additional ribs are preferably provided as shown toward the right of the diagram of Fig. 12, which ribs have the sarne profile as the ribs 80a, b and c and serve to finish off and planish the thread formed on the finished blank. A study of Fig. 12 will show that the bulk of the metal deforming action is performed by the ribs 18a, '19a and 80a, whereas the ribs of the second and third rollers corresponding to these ribs merely serve to finish olf and to perfect the prole of the formed thread at each step. It will'be realized also that the ribs 11a, ''lb and 'l'lc firmly support the blank entering the threading head at three points 120 apart about its circumference before any of the deforming ribs of the roller dies begin to work upon the blank. This prevents flexing of the blank where it enters the threading head and contributes to the accuracy of the work performed.

A further modification of the roller dies illustrated in Fig. 13 divides the work among a. still greater number of roller die ribs. This diagram is similar to that of Fig. 12 in that the profile of the first roller is shown in full lines, that of the second roller in dot-dash lines, and that of the third roller in dash lines. Preferably the first rib on each of the three rollers indicated at 82a, B2b and 82o perform the same function as the ribs 11 of Fig. 12, namely, they are intended to be in firm contact with the surface of the blank without appreciably entering it. This supports the end of the blank where it enters the threading head, it being understood that the remote end of the blank is gripped in a slidable tailstock as Vpreviously' described. The rib 83a of roller No. 1 has a crest radius equal to that of the ribs 82a, b and c plus one-eighteenth of the depth of thread. Rib 83h on the second roller has a crest radius which is one-eighteenth of the depth of thread greater than the radius at 83a. In like manner the rib at 83C on the third roller is oneeighteenth of the depth of thread greater in radius than that at 83h. In a similar manner the ribs 84a, b and c (one on each roller) increases in each case by one-eighteenth of the depth of thread, and the rollers 85 in a like manner, so that when the crest 85e is reached the rib is rolling to the root of the thread formed on the blank. In other words, the work of forming the thread groove is divided substantially equally among the nine ribs from 83a to 85C. It Will be understood that as the crests of the ribs on the roller dies enter deeper and deeper into the blank, the metal of the blank flows outwardly between the ribs of the roller dies until it finally fills the grooves on the roller dies out to the point 86 to complete the crest of the thread formed on the blank. The additional ribs at the right of Fig. 13 are for finishing and planishing the threads formed in the Work piece. Thus a device using the roller dies of Fig. 13 .will form the thread very gradually in the Work piece so that smooth flow of metal is assured with a minimum of friction between the blank and the dies, resulting in a very nicely finished thread without any grooving at the crest of the thread in the blank. Such a thread is very strong because the bers or ble therewith is a pinion 9i.

Acrystals of the metal are arranged evenly along the contours of the thread and parallel to the finished profile and the metal is denser at the wearing surface because of the compression applied and this density is substantially uniform because of the step-by-step formation of the thread due to the spreading of the work over a number of roller dies ribs.

One of the essentials to the formation of an accurate thread by this apparatus is the accurate spacing of adjacent ribs on a roller die to the exact pitch of the thread to be y)formed on the blank. To this end we carefully grind the roller dies to their finished profile with substantially no tolerance and to an accuracy preferably within .0001 of an inch or better.

We may arrange our roller dies with otherv novel means for supporting the blank where it enters the dies and for also truing up the size of the blank before it enters the dies. Such an embodiment is indicated in very great enlargement in Fig. 14 showing the profile of one end of one of the roller dies. The entering end of this roller die is provided with a cylindrical surface 91 preceding the thread forming ribs 88 which are similar to 'those previously described. The portions 8l engage the surface of the blank at spaced points on the circumference of the blank, the various surfaces 8l being located to correspond to the pitch diameter or effective diameter of the thread to be rolled in the blank. Thus if the blank has slight variations from the true pitch diameter'desired, the portions 8l rolling upon that surface will tend to true it up. At the same time they hold the 'blank rmly when the rst thread rolling ribs begin to operate,

A modification of our device is shown in Figs. 15 to 19 wherein the roller dies are set on axes substantially parallel to the axis of the head and each roller carries helically formed ribs correspending to the thread to be rolled in the blank. This type of apparatus is useful where Very heavy work has to be done on a blank to deform certain types of thread therein, or where the helix angle of the thread to be formed on the blank is so great that there would be intense friction between the roller dies and the blank if arranged according to the 'lirst modification described. Parts shown in Figs. 15 and 16 which are similar and analogous in function to those already described will be given similar reference characteristics and only the differences will be described here. Three roller dies are provided as before, equally spaced 120 apart about the axis of the head. These roller dies are shown at B9 and one is shown very much enlarged in Figs. 17 and 18. Each roller die is keyed to a shaft 9U which is set in the roller holder i9 on an axis parallel to the axis of the head. The shaft therefore has bearings in the arms Mid of the holder. A portion of shaft 9G overhangs toward the rear of the head and pressed on this shaft so as to be rotata- It is necesary to maintain a coordinated rotation between the three roller dies in this form of our device so as to insure the helical ribs of the dies always tracing the proper path on the blankl Therefore we have provided a ring gear 92 meshing with the three pinions 9i as shown in Fig. 16. This ring gear has a bearing on an extension of bushing 93 which is the internal bushing of the barrel 21 and is freely rotatable thereon.

Each roller die in this form of the device has a portion 93' first engaging the blank on its pitch diameter or effective diameter to firmly support the blank for the thread rolling operation. The helical rib 94 on the roller die then begins at said eifective diameter and gradually increases throughout several complete spirals, preferably three or more, until approximately the point has been reached Where the ribs are of suiicient diameter to roll to the root of the thread on the blank. Here as in the previous instances the material of the blank flows outwardly between the ribs of the roller dies until it reaches the outside diameter of the thread on the blank. It is understood that the helical ribs on the three rollers may be alike so that the rst engaging roller does the bulk of the work and the other two give a planishing action in an analogous manner to the action described in connection with Fig. 12. On the other hand the ribs of the second and third rollers may be stepped up so that corresponding portions of the ribs each deepen the thread in the work blank in a manner analogous to the action described in connection with Fig. 13. Of course it is necessary to begin the helical rib farther along the second and third rollers so that the first portions of each rib to engage the blank are spaced in a helical path about the axis of the head corresponding tothe helix formed on the threaded blank. In other words corresponding parts of the various roller dies trace the same helical path on the blank. It should be obvious that the ring gear 92 meshing with the pinions 9i always insures this relation after the parts have been assembled.

The device of Figs. 15 to 19 is adapted to have the roller dies moved radially inwardly and outwardly by relative longitudinal movement between the die ring 32 and the blocks 38 as pre Viously described. It is important that the relationship 'between pinions 9i should not vary during such opening and closing movement of the dies. Fig. 19 shows diagrammatically a portion of ring gear 92 and one of the gears 9| in full lines in meshed position corresponding to closed. position of the head when the roller dies are working on a blank. In dot-dash lines there is shown the relative position of each of the pinions 9| with respect to the gear 92 when the head is open. It will be seen that the pinions and the central gear are still in mesh so that they cannot lose their relative positions. We prefer involute teeth on the gear and pinions. It will be realized that the rod 15 or its equivalent is utilized in connection with the rolling head shown at Fig. 15 to limit the opening movement of the dies so that the condititon shown in Fig. 19 always prevails, If there is any back lash between gear 92 and pinions 9| it is taken up as soon as the portions 93 of the roller dies engage the blank so that there is always an exact relation between the various roller dies when they first start to roll the thread in the blank. It need hardly be said that the pitch of the ribs on the dies 89 is formed with accuracy equal t0 that described in connection with the first modifcation.

In both modifications the roller dies are securely held against movement radially outwardly, once they are set, so that accurate threads are rolled. The means by which this is accomplished include suicient bearing surface between the roller dies and shaft 49 or 30 and between the shaft and hold 40, the holders are firmly held in blocks 38 and the latter in ring 32 which is quite heavy. Ring 32 is provided with outwardly projecting lips 32h overhanging each roller die support to additionally resist radial movement outward.

What we claim is:

1.` Means for rolling threads in a substantially cylindrical blank comprising a head having a centrally located opening for passing said blank therethrough, a plurality of roller dies rotatably mounted in said head about said opening, there being ribs on said dies for rollingdepressions in a blank to the root of the thread to be formed on it, said ribs having profiles corresponding to the prole of the thread to be rolled by them, there being a plurality of ribs on each die spaced apart with the pitch of the thread to be rolled, the portions of the ribsof said dies nearest the axis of said head being arranged about said axis in a helical path corresponding to the helix of the thread to be formed on said blank, there being a plurality of said ribs having their crests located progressively nearer the axis of said head and adaptedl to enter the material of the blank to roll a thread thereon, and the crests of ribs on one die being of height intermediate the crests of ribs on the other dies preceding and following it along said helical path.

2. Means for rolling threads in a substantially 'cylindrical blank comprising a head having a centrally located opening for passing said blank of said dies being spaced along said head and cirf curnferentially about said blank opening in a helical path corresponding to the helix of the thread to be formed on said blank, there being at least three of said ribs on each die having their crests located progressively nearer the axis of said head and adapted to enter the material of the blank to roll a thread thereon, all of said ribs havmg the same flank angle as the thread to be rolled, and means for causing relative rotation between said head and dies.

3. Means for rolling threads in a substantially cylindrical blank comprising a rotatable head having a centrally located opening for receiving said blank, a plurality of roller dies rotatably mounted in said head about said opening, there being ribs on said dies for rolling depressions in a blank to the root of the thread to be formed on it, said ribs being annularly arranged on said dies and spaced apart according to the pitch of the thread to be rolled, said rollers being set in said head at an angle to its axis corresponding to the helix angle of the thread to be rolled, there beingV a plurality of said dies spaced circumferentially about the axis of said head, the ribs on each of said dies being arranged to trace the same helical path on a blank, there being successively engaging ribs on one of said dies of progressively greater crest diameter and corresponding ribs on another of said dies having crest diameters intermediate the corresponding diameters on said one ldie so that a thread on the blank is deepened alternately by a rib on one die and then the other whereby each rib deepens the depression made by the rib which preceded it.

4. Means for rolling threads in a substantially cylindrical blank comprising a rotatable head having a centrally located opening for receiving said blank, a plurality of roller dies rotatably mounted in said head about said opening, there being ribs on said dies for rolling depressions in a blank to the root of the thread to be formed on it, said ribs being annularly arranged on said dies and spaced apart according to the pitch of the thread to be rolled, said rollers being set in said head at an angle to its axis corresponding to the helix angle of the thread to be rolled, there being three of said dies spaced one hundred and twenty degrees apart about the axis of said head, the ribs on all of said dies being arranged to -trace the same helical path on a blank, there being a first-engaging rib on a rst of said rollers, a second-engaging rib on a second of said rollers and having a crest diameter greater than the crest diameter of said rst-engaging rib, a thirdengaging rib on the third of said rollers and having a crest diameter greater than the crest diameter of said second-engaging rib, and a fourth engaging rib on the rst of said rollers and having a greater crest diameter than the crest diameter of said third-engaging rib, whereby each rib progressively rolls the thread deeper into the blank, and means for rotating said head.

5. Means for rolling threads in a substantially cylindrical blank comprising a rotatable head having a centrally located opening for receiving said blank, a plurality of roller dies rotatably mounted in said head about said opening on axes substantially parallel to the axis of said head, there being helical ribs on said dies corresponding to the thread to be rolled in said blank, said ribs on the different rollers at the blank-entering end of said head being spaced apart by substantially the diameter of said blank, said ribs gradually increasing in height along their helices so as to progressively enter said blank by greater amounts up to the root diameter of the thread to be formed on said blank, means coordinating the movement of said rollers so that said ribs on the different rollers follow the same helical path on said blank, the rib on one of said rollers having a greater crest diameter than the crest diameter of that portion of the rib preceding it which traces the same part of the thread in the blank, whereby rst one roller and then another deepens the thread groove in the blank, and means for rotating said head.

-6. Means for rolling threads in a substantially cylindrical blank comprising a rotatable heud having a centrally located opening for receiving said blank, a plurality of holders mounted in said head for movement radially thereof, means for moving said holders radially, a shaft rotatably mounted in each holder, a roller die and a pinion on each shaft connected to rotate together, said roller dies having ribs adapted to roll a thread in the blank, a gear mounted in said head for free rotation radially inwardly from said pinions and meshing with all of said pinions. the coacting teeth on said gear and pinions being of a length to maintain meshing relation upon radial movement of said holders and dies sullicient to remove said ribs from the thread in the blank, and means for rotating said head.

MERLE W. LAMPRECHT. HAROLD N. ANDERSON. 

